The performance of parallel combinatory spread spectrum (PC/SS) communication systems in the frequency-nonselective, slowly Rayleigh fading channel is studied. Performance is evaluated by symbol error rate using numerical computation. To overcome the performance degradation caused by fading, we also studied the effects of selection diversity and Reed-Solomon coding applied to the PC/SS system. As a result, a remarkable improvement in error rate performance is achieved with Reed-Solomon coding and diversity technique. The coding rate for the maximum coding gain is almost a half of that in the additive white gaussian noise channel.

Data of system parameters of real systems have some uncertainty and they should be given by sets (or intervals) rather than fixed values. To analyze and design systems contaning such uncertain parameters, it is required to represent and treat uncertainty in data of parameters, and to compute value sets of characteristic polynomials and transfer functions. Interval arithmetic is one of the most powerful tools to perform such subjects. In this paper, Polygon Interval Arithmetic (PIA) on the set of polygons in the complex plane is considered, and the data structure and algorithms to execute PIA efficiently is proposed. Moreover, practical examples are shown to demonstrate how PIA is useful to compute the evaluation of value sets.

It is well known that weather conditions affect the performance of satellite broadcasting receiving systems. For example, snow accretion on antennas degrades the receiving performance seriously because it reduces received signal power and also can increase antenna noise. Since effects of the weather are considered to differ for various types of receiving antenna, an investigation on this phenomenon is very important. A study on weather effects to three types of satellite broadcasting receiving antenna, a planar antenna, a center-fed parabolic reflector antenna, and an offset parabolic reflector antenna, is presented in this paper. Since the performance of receiving antennas can be determined by a parameter G/T, a long-term and continuous measurement of G/T must be performed. Furthermore, the measurement of more than one receiving system should be performed simultaneously. Also, the measurement should be performed in a snowy area (in winter) and a rainy area (in the other seasons) to evaluate the effect of the weather. To fulfil the criterion, a continuous measurement system of G/T has been built in Hokkaido University, Sapporo. Sapporo, which is located at latitude 42 degrees north, has a long and snowy winter, and also has rainy days in the other seasons so that we can evaluate the effect of weather. Using this measurement system, cumulative distributions of measurement results are obtained so that the performance of different types of receiving system can be evaluated. In this paper, some considerations on the noise level are also discussed briefly to evaluate the performance degradation of the receiving systems.

New communication systems via chaotic modulations are experimentally, demonstrated. They contain the wellknown chaotic circuits as its basic elements--Chua's circuits and canonial Chua's circuits. The following advantage is found in our laboratory experiments: (a) Transmitted signals have broad spectra. (b) Secure communications are possible in the sense that the better parameter matching is required in order to recover the signal. (c) The circuit structure of our communication system is most simple at this stage. (d) The communication systems are easily built at a small outlay.

This paper presents an optimal filtering algorithm using the covariance information in linear continuous distributed parameter systems. It is assumed that the signal is observed with additive white Gaussian noise. The autocovariance function of the signal, the variance of white Gaussian noise, the observed value and the observation matrix are used in the filtering algorithm. Then, the current filter has an advantage that it can be applied to the case where a partial differential equation, which generates the signal process, is unknown.

A novel analysis method of the intermodulation (IM) and the noise power ratio (NPR) of multiple-carrier amplifiers is descrided. This method, based on Discrete Fourier Transform, allows an accurate calculation of IM and NPR of the amplifier having multiple carriers by directly using measured single-carrier amplitude and phase characteristics. This method has an outstanding feature in that it can be applied to the general case of n carriers having an arbitrary power level as long as frequency-dependence of amplitude and phase characteristics is negligibly small. Applying this method to the linearized amplifier, a good agreement between measured and calculated results for IM3, IM5, and NPR has been obtained for operation from linear up to saturation, which shows this method would be a good candidate for calculating IM and NPR of multiple-carrier amplifiers.

This paper describes a nondestructive measurement method for complex permittivity of dielectric material at pseudo microwave frequencies. The resonator used in this study has a cylindrical cavity filled with a sapphire material of a well known complex permittivity. The resonator is divided into two parts at the center. A dielectric substrate specimen is clamped with these halves. Relative permittivity εand loss tangent tan δ of the specimen are obtained at 3 GHz using the TE011 resonance mode. The accuracy of the present method is evaluated through the comparison of the measured values by the new method with those at around 10 GHz by the conventional empty cavity resonator method. The errors of measurements are smaller than 1% and 1105 for εand tan δ, respectively.

A new efficient waveform relaxation technique based on dynamically overlapped partitioning scheme is presented. This overlapped partitioning method enables the application of waveform relaxation technique to bipolar VLSI circuits. Instead of fixed overlapping, we select the depth of overlapping dynamically based on the sensitivity criteria. By minimizing the overlapped area, we could reduce the additional computational overhead which results from overlapping the partitions. This overlapped waveform relaxation method has better convergence properties due to smaller error introduced at each step compared with standard relaxation techniques. When overlapped partitioning is used in the case of digital circuits, the waveforms obtained after first iteration are nearly accurate. Therefore, by using these waveforms as initial guess waveforms for the second iterations we can reduce Newton-Raphson iterations at each time point.

A noninvasive method for measuring complex permittivity of biological tissues is proposed. The noninvasive method is based on an inverse scattering technique which employs an iterative procedure. The iterative procedure consists of solving an electric field integral equation using the method of moments and minimizing the square difference between calculated and measured scattered fields. Implementation of the noninvasive method requires the knowledge of the target shape, the incident and measured scattered fields. Based on the noninvasive method, a measuring system of complex permittivity is developed and its reliability is verified.

It is important to obtain a low coefficient sensitivity digital filter. This paper presents a new low coefficient sensitivity network structure that consists of a second order digital filter and a feedback path. This network structure is based on the effectiveness of the feedback path in an analog system. The coefficient sensitivity of the proposed digital filter can be control with the coefficient of the feedback path. Using this property, the digital filter with the low coefficient sensitivity is obtained. To add the feedback path makes the frequency response deviate from the characteristic of the original second order digital filter, but the deviation can be compensated with the other coefficients. A nonlinear optimization technique is employed to determine the coefficients of the digital filter. The proposed method is not effective only to narrow-band low-pass but wide-band low-pass filters.

This paper presents an experimental study on the penetration characteristics of submillimeter waves in biological tissues and material. The measured values of the penetration depth in excised natural muscle, fat, and aqueous solution of protein, bovine serum albumin (BSA), over the wavelengths of 281 through 496µm are presented. Penetration depths at these wavelengths are 0.11-0.17mm in the natural pork muscle, and 0.69-0.98mm in the natural pork fat, and are the larger at the longer wavelengths. The values vary considerably from sample to sample. Since the measurement of the penetration depth in this study is shown sufficiently reproducible, the variation of the measured penetration depth is attributed to the variation of natural tissues such as that in water content. It is found that the penetration depth of submillimeter waves in aqueous solution of BSA depends almost linearly on the amount of protein content in the solution, and that the typical values of the penetration depth in the natural muscle roughly agree with that in the 35% aqueous solution of BSA in the submillimeter-wave region.

We describe a new water sensing system for optical fiber cable networks. This system consists of optical fibers, water sensors and an OTDR (Optical Time Domain Reflectometer). The water sensor contains material which swells on contact with water and bends the optical fiber. The OTDR monitors the optical loss increase caused by this fiber bending and determines its location. In this system it is very important to determine the loss increase caused by the water sensor in terms of the OTDR performance. Therefore, we clarified the relationship between the water sensor structure and the increase in loss. Based on this study, we fabricated a sensor which causes a 5dB loss increase. The measured value is very close to the calculated value.

The effect of intersymbol interference resulting from non-matched receiver filtering on the bit error rate (BER) performance of π/4-DQPSK systems recently adopted in the North American and Japanese digital cellular standards, is analyzed in Rayleigh fading. With a Gaussian or a Butterworth (of order N, 2N10) receiver filter, the BER performance is found to degrade by only a small fraction of a decibel from the performance with ideally matched receiver filters. A 4th-order Butterworth receiver filter leads to BER curves which almost coincide with those of the ideally matched filtering condition.

From the standpoint of studying the biological effects of microwaves on human eyes, this paper numerically examines the specific absorption rate (SAR) inside the eyeball, using the finite-difference time-domain (FD-TD) method, which does not require very much computer storage. Two kinds of highly heterogeneous models constructed by us and Taflove's group are used to compute the SARs inside the eyeball for 1.5-GHz microwave exposure under the 1991 ANSI protection guideline. The SAR contour lines and the spatial distribution are shown inside the eyeball. Comparison is also made between the SARs for the two computation models.

This paper surveys the researches on biological and electeromagnetic environments in RF (radio frequency) and microwave regions in Japan. Publicized research reports on biological objectives, evaluation of exposure rate, electromagnetic environments and guideline for the protection from radio wave nuisances are briefly introduced. Some researches on the evaluation of the exposure rate caused by the near field effect of portable radio transceiver are reviewed. Radio frequency exposer protection guidelines in Japan are also described.

This paper theoretically and experimentally investigates the mutual coupling between two ports of dual slot-coupled circular microstrip antennas. Presented are the effects of feed configuration, slot length, slot offset from the circular disk center, circular disk radius and the dielectric constant of the feed substrate on the mutual coupling. Based on these results, the antenna with low mutual coupling was designed. The mutual coupling of under -35dB at the resonant frequency was obtained.

We developed an automatic data processing algorithm for a ground-probing radar which is essential in analyzing a large amount of data by a non-expert. Its aim is to obtain an optimum result that the conventional technique can give, without the assistance of an experienced operator. The algorithm is general except that it postulates the existence of at least one isolated target in the radar image. The raw images of underground objects are compressed in the vertical and the horizontal directions by using a pulse-compression filter and the aperture synthesis technique, respectively. The test function needed to configure the compression filter is automatically selected from the given image. The sensitivity of the compression filter is adjusted to minimize the magnitude of spurious responses. The propagation velocity needed to perform the aperture synthesis is determined by fitting a hyperbola to the selected echo trace. We verified the algorithm by applying it to the data obtained at two test sites with different magnitude of clutter echoes.

The biological effects of power frequency electric and magnetic fields have been a source of concern for the past many years, especially since 1979 when an epidemiological study report suggested a positive relationship between childhood cancer and exposure to power frequency electromagnetic fields from residential overhead power lines. The extensive studies of dosimetry and biological effects have since been carried out. It is believed that power frequency electromagnetic fields does induce biological effects (no serious threat to human health). The clear explanations for the possible interaction mechanisms remain to be identified. The problem with the study on dosimetry has been lack of theory that applies to the physical interaction of power frequency electric and magnetic fields with humans. At present, it seems to be widely accepted that the density of induced currents in the human body can be used as the decisive parameter in evaluating human exposure to these fields. In order to predict the distribution of induced current density inside a human body exposed to electric fields, magnetic fields, or electric and magnetic fields that coexist, the precise measurements of electromagnetic environments are necessary. According to necessity, the fields have to be characterized in terms of strength, orientation and phase angle. This paper presents: (1) Measurements of power frequency electromagnetic environments in 187kV substation yard and in the vicinity of the ground under 187 kV line using laboratory-made instruments; (2) Development of magnetic field exposure monitor; and (3) Review of state of the art of theoretical dosimetry for electric fields, magnetic fields and combined electric and magnetic fields, and evaluation method of human exposure for the future research.

Artificial Neural Networks (ANN's) that are able to learn exhibit many interesting features making them suitable to be applied in several fields such as pattern recognition, computer vision and so forth. Learning a given input-output mapping can be regarded as a problem of approximating a multivariate function. In this paper we will report a theoretical framework for approximation, based on the well known sequences of functions named approximate identities. In particular, it is proven that such sequences are able to approximate a generally continuous function to any degree of accuracy. On the basis of these theoretical results, it is shown that the proposed approximation scheme maps into a class of networks which can efficiently be implemented with analog MOS VLSI or BJT integrated circuits. To prove the validity of the proposed approach a series of results is reported.

The dielectric resonator method is now widely accepted as a precise measurement method for determining the dielectric properties at microwave frequencies. This paper describes the measurement results of εr, tan δ and TCf determined by a round robin test of this method. The resultant measurement errors were Δεr/εr0.10%, Δtan δ0.5105 and ΔTCf0.5 ppm/K, where Δdenotes a standard deviation. The causes of measurement errors and the conditions to improve the measurement accuracy are discussed.